1. Technical Field of the Invention
The present invention relates to a liquid crystal device, an electronic device and a method of manufacturing the liquid crystal device, and more specifically, the present invention relates to the structure of a liquid crystal device comprising a reflecting layer provided on one of two substrates which constitute the liquid crystal device.
2. Description of the Related Art
A reflective liquid crystal display device is conventionally widely used, in which a display can be visualized by using external light. This reflective liquid crystal display device eliminates the need for a light source such as a back light or the like, and thus has the advantage that the power consumption can be decreased, and the size and weight can easily be decreased, as compared with a transmissive liquid crystal display device. Therefore, the reflective liquid crystal display device is widely used for portable devices, etc. Also, a transflective liquid crystal display device which can be used as a reflective liquid crystal display device with external light, and which can visualize a display by using light of a back light in the dark, and a liquid crystal display device with a front light which can visualize a display by using light from the front light have been developed.
The reflective or transflective liquid crystal display device or the liquid crystal display device with a front light comprises a reflecting layer provided under a liquid crystal layer, for reflecting light incident from the observation side. In this case, the reflecting layer having a mirror plane as a reflecting plane causes reflection of a background, and room illumination, etc., thereby causing the problem of making a display image hard to see. In order to solve this problem, a method is conventionally used, in which a surface of the reflecting layer is roughened to appropriately scatter reflected light.
As a conventionally used method for roughening the surface of the reflecting layer, for example, a roughening method for roughening a surface of the reflecting layer is known, in which the substrate surface is polished and roughened by an abrasive and a metal film is formed on the roughened surface.
However, in a liquid crystal device comprising a reflecting layer having the conventional roughened surface, a surface of a substrate is totally roughened, and alignment marks, switching elements, a sealing material, etc., which should be formed on a flat surface of a substrate, are inevitably formed on the roughened surface of the substrate, thereby causing the problem of deteriorating mark visibility, or causing a defect in the operation of the switching elements, a defect in sealing, or the like.
Also, the surface of the reflecting layer is regularly roughened to produce interference in reflected light, thereby causing the problem of coloring an image. Ideally, the surface of the reflecting layer is irregularly roughened to form an irregularly roughened surface. However, it is very difficult to finely control the state of surface roughness in order to form the irregularly roughened surface.
A possible method for solving the above problem comprises etching or chemically polishing a portion of the surface of a substrate to form an irregularly roughened surface. However, in such partial chemical processing of the surface of the substrate, the roughened surface area (referred to as a xe2x80x9croughened surface areaxe2x80x9d hereinafter) is recessed, as compared with a flat surface area (referred to as a xe2x80x9cflat surface areaxe2x80x9d hereinafter). Therefore, in dispersing a spacer for regulating a cell gap between two substrate, the spacer extends to the flat surface area or mixes with a sealing material to increase the cell gap in the periphery of a liquid crystal display area. This possibly causes a variation in display contrast, or the like due to nonuniformity in the cell gap.
Accordingly, the present invention has been achieved for solving the above problem, and an object of the present invention is to provide a liquid crystal device comprising a reflecting layer having a conventional roughened reflecting plane, and a novel cell structure capable of decreasing an optical defect and a defect in the cell structure due to the roughened reflecting plane.
A liquid crystal device of the present invention comprises a liquid crystal sandwiched between two substrates, a roughened surface area and a flat surface area which are formed on a surface of one of the substrates opposite to the other substrate, and a reflecting layer formed on the roughened surface area, wherein the reference plane of the roughened surface area is lower than the surface of the flat surface area.
Particularly, in the present invention, the total thickness of a surface structure selectively formed on the roughened surface area of one of the substrates and a surface structure selectively formed on the area of the other substrate opposite the roughened surface area is equivalent to or larger than the step difference between the reference plane height of the roughened surface area and the surface height of the flat surface area.
The terms xe2x80x9cselectively formed on the roughened surface areaxe2x80x9d mean substantially no formation on the flat surface area, and the terms xe2x80x9cselectively formed on the area of the substrate opposite to the roughened surface areaxe2x80x9d mean substantially no formation on the region opposite to the flat surface region.
In the present invention, the reference plane of the roughened surface area is lower than the surface of the flat surface area, but the total of the thickness of the surface structure selectively formed on the roughened surface area of one of the substrates and the thickness of the surface structure selectively formed on the area of the other substrate opposite the roughened surface area is equivalent to or larger than the step difference between the roughened surface area and the flat surface area. Therefore, the distance between the substrates in the roughened surface area comprising the reflecting layer can be made equivalent to or smaller than that in the flat surface area.
Therefore, in regulating the space between both substrates by control means such as a spacer or the like, the distance between the substrates in the roughened surface area can be accurately regulated by the control means, and thus an optical function portion comprising the reflecting layer having a roughened surface can be precisely formed. In this case, the step difference between the reference plane height of the roughened surface area and the surface height of the flat surface area can be freely set to some extent, thereby permitting the preferred roughness state of the roughened surface area to be easily formed without great restriction.
In the present invention, the total of the thickness of the surface structure selectively formed on the roughened surface area of one of the substrates and the thickness of the surface structure selectively formed on the area of the other substrate opposite the roughened surface area is preferably larger than the step difference between the roughened surface area and the flat surface area.
As another aspect of the present invention, a liquid crystal device comprises a predetermined surface structure formed on one of two substrates, wherein the surface height of the substrate including the surface structure in the roughened surface area is equivalent to or larger than that in the flat surface area. In this case, the surface of the substrate including the surface structure in the roughened surface area is preferably higher than that in the flat surface area.
As a further aspect of the present invention, a liquid crystal device comprises a colored layer and a protecting layer laminated in turn on a reflecting layer, or an insulating layer formed on the reflecting layer, wherein the total thickness of the reflecting layer, the colored layer and the protecting layer, or the total thickness of the reflecting layer and the insulating layer is equivalent to or larger than the step difference between the reference plane height of the roughened surface area and the surface height of the flat surface area. In this case, the total thickness of the layers is preferably larger than the step difference between the reference plane height of the roughened surface area and the surface height of the flat surface area.
In the present invention, the two substrates are bonded together through a sealing material, and regulation means is arranged inboard of the sealing material, for regulating the distance between the substrates. The regulation dimension of the regulation means is preferably smaller than the thickness of the sealing material. Since the regulation dimension of the regulation means is smaller than the thickness of the sealing material, the influence of the regulation dimension of the regulation means on the thickness of the sealing material can be decreased even when the regulation means is arranged on the flat surface area or arranged inside the sealing material, thereby decreasing a variation in the distance between the substrates.
In the present invention, another regulation means is provided within the sealing material for regulating the thickness of the sealing material. By regulating the thickness of the sealing material by the other regulation means, the distance between the substrates can be made uniform with high precision over the entire liquid crystal device. In this case, the regulation dimension of the regulation means provided inboard of the sealing material is smaller than the regulation dimension of the other regulation means provided within the sealing material.
The regulation means and the other regulation means comprise a spherical or cylindrical spacer having an outer diameter for determining the regulation dimension.
As a further aspect of the present invention, a liquid crystal device comprises two substrates bonded together with a sealing material provided therebetween, and a liquid crystal arranged inside the sealing material, wherein a roughened surface area and a flat surface area are formed on a surface of one of the substrates opposite to the other substrate so that the reference plane of the roughened surface area is lower than the surface of the flat surface area, a reflecting layer is formed on the roughened surface area, the sealing material is arranged on the flat surface area, and the thickness of the sealing material is equivalent to or larger than the thickness of the liquid crystal layer in the roughened surface area. In this case, the thickness of the sealing material is preferably larger than the thickness of the liquid crystal layer in the roughened surface area.
In the present invention, regulation means is arranged inboard of the sealing material, for regulating the distance between the substrates, and the regulation dimension of the regulation means is preferably smaller than the thickness of the sealing material. In this case, another regulation means is preferably provided within the sealing material, for regulating the thickness of the sealing material.
An electronic device comprises any one of the above-described liquid crystal devices preferably serving as display means. Particularly, since a reflecting or transflective liquid crystal device with low power consumption comprising a reflecting layer can be constructed, an electronic device is preferably a potable electronic device such as a portable information terminal, a portable telephone, a pager, or a portable watch (a wrist watch, a pocket watch, or the like).
A method of manufacturing a liquid crystal device of the present invention comprising a liquid crystal sandwiched between two substrates comprises forming a roughened surface area and a flat surface area on a surface of one of the substrates opposite the other substrate so that the reference plane of the roughened surface area is lower than the surface of the flat surface area, selectively forming a surface structure on the roughened surface area of the one of the substrates and a surface structure on the area of the other substrate opposite the roughened surface area so that the total thickness of the surface structures is equivalent to or lager than the step difference between the reference plane height of the roughened surface area and the surface height of the flat surface area, and then bonding together the two substrates with a sealing material arranged on the flat surface area.
Another method of manufacturing a liquid crystal device of the present invention including a liquid crystal sandwiched between two substrates comprises forming a roughened surface area and a flat surface area on a surface of one of the substrates opposite the other substrate so that the reference plane of the roughened surface area is lower than the surface of the flat surface area, forming a surface structure on each of the roughened surface area of the one of the substrates and the area of the other substrate opposite the roughened surface area, and then bonding together the two substrates with a sealing material arranged on the flat surface area so that the thickness of the sealing material is larger than the thickness of the liquid crystal layer in the roughened surface area.
The present invention preferably comprises the step of covering a portion of the surface of one of the substrates with a mask, roughening the exposed portion of the surface, and then removing the mask to form the roughened surface area and the flat surface area.
The present invention preferably further comprises the step of further processing the roughened surface by another method to change the shape of the surface irregularity in the roughened surface area after the roughening step. This can bring the shape of the surface irregularity of the roughened surface area close to a shape that can realize a reflecting plane having an optically preferable roughness state. In this case, the step of changing the shape of the surface irregularity of the roughened surface area is performed after the mask is removed, thereby decreasing the step difference between the reference plane height of the roughened surface area and the surface height of the flat surface area.
In the present invention, one of the two substrates preferably includes regulation means for regulating the distance between the substrates, and bonded with the other substrate with the sealing material provided therebetween so that the thickness of the sealing material is larger than the regulation dimension of the regulation means.
In the present invention, the sealing material preferably includes another regulation means therein having a regulation dimension larger than the regulation dimension of the above-described regulation means so that the two substrates are bonded together with the thickness of the sealing material regulated by the regulation dimension of the other regulation means.